Absence of coherent peaks in a Z2 fractionalized BCS superconducting state

We explore a Z(2) fractionalized Bardeen-Cooper-Schrieffer (BCS) superconducting slate, which is a minimal extension of usual BCS framework. It is found that this state has similar thermal and transport properties, but its single-particle feature strongly deviates from the coherent quasiparticle behavior of the classic/conventional BCS superconducting state. The Fingerprint of such Z(2) BCS state is the absence of the BCS coherent peaks and instead a kink in the local density of state occurs, which in principle could be probed by scanning tunneling microscopy or point-contact spectroscopy experiments. The corresponding exactly soluble models that realize the desirable Z(2) fractionalized BCS state are presented. In addition, we also study the extended t-U-J model by using Z(2) slave-spin representation and Find that the Z(2) BCS state may exist when the paring structure is fully gapped or has nodes. The prototypical wave-function of such a Z(2) BCS state is also proposed, which could be taken as trial wave-function in current numerical techniques. Furthermore, the pairing mechanism of Z(2) BCS state is argued from both weak and strong coupling perspective. The present work may be helpful to further study the unconventional superconductivity and its relation to non-Fermi liquids. (C) 2014 Elsevier By. All rights reserved.